1. Field of the Invention
The present invention relates to an improvement in a lens barrel including a plurality of lenses and a lens driving apparatus or zoom lens driving apparatus configured to drive the lenses from a collapsed position to a photographic or extended position, and a camera including the lens barrel, more specifically to a lens barrel including a lens driving apparatus or zoom lens driving apparatus capable of performing stable operation without backlash.
2. Description of Related Art
In recent years, each of a large number of lens barrels used to photograph is mainly applied for a zoom lens configured to vary a focal distance continuously by changing positions of a plurality of lens groups in photographing. On the other hand, in case of non-photograph, the lens barrel is mainly used as a miniaturized collapsable-type-zoom lens barrel in which the lens groups are accommodated in a fixed cylinder of the lens barrel by moving relatively the lens groups so that small intervals are set among the lens groups.
Such a lens barrel includes a lens moving structure in which a rotational cylinder is attached to the fixed cylinder and lens frames are moved in a direction of an optical axis through a cam or helicoidal engagement structure when the rotational cylinder is rotated relative to the fixed cylinder.
The lens moving structure has a typical mechanism in which a rotational cylinder is engaged with a fixed cylinder through a cam structure so that the rotational cylinder rotates and forwardly and backwardly moves through the cam structure. The lens moving structure includes a linearly moving guide cylinder which is disposed in the rotational cylinder, rotatable relative to the rotational cylinder and moves together with the rotational cylinder in a direction of an optical axis and lens frames which are disposed in the linearly moving guide cylinder and configured to hold a plurality of lenses, respectively. Each of the lens frames has a cam follower which passes through a linearly moving groove of the linearly moving guide cylinder extending in the optical axial direction and engages with a cam groove provided in an inner surface of the rotational cylinder.
When the rotational cylinder is rotated, the lenses can be moved to any position within a movable range without being rotated. For example, a rotational key provided on the linearly moving guide cylinder to radially project is engaged in a peripherally extending rotational groove provided in the inner surface of the rotational cylinder, thereby the linearly moving guide cylinder can be rotated about an optical axis relative to the rotational cylinder, but can be moved together with the rotational cylinder in the optical axial direction.
A lens barrel needs to align an optical axis of each lens group in order to maintain image-focusing property. However, as the number of driving parts to move lenses increases, it is difficult to align the optical axis of each lens. As the lend barrel is downsized, it is required to enhance accuracy for alignment of the optical axis of each lens.
As a method for aligning the optical axis of each lens, it is proposed to hold two lens group frames with an inner diameter of one lens group frame (for reference, see Japanese Patent Application Publication No. 2003-270509). According to a technology as disclosed in Japanese Patent Application Publication No. 2003-270509, coaxial performance of a first lens group and a second lens group is maintained with relatively high accuracy. However, because one lens frame is supported by a rotational cylinder and a linearly moving guide cylinder, fall over of the lenses due to a backlash generated in these parts occurs.
Consequently, it is not possible to align the optical axis of each lens. Also, there is known a technology configured to compensate lens frames to a correct position from a deviated position by use of springs biasing each of the lenses (for reference, see Japanese Patent Application Publication No. 2006-071844). However, there is a problem that when each lens is in a collapsed potion, a biasing force is applied to structural parts, a large energy is required to move the lens frames and so on between the collapsed position and a photographic position.